Resistor bulb



Feb. 14, 195o G. D, CERF",

RESISTOR BULB Filed Aug. 8, 1947 Buncntor GuSax/'e D- Cerf' (ttorncg Patented Feb. 14, 1950 RESISTOR BULB Gustave D. Cerf, Livingston, N. J., assgnor, by

mesne assignments, to Thomas A. Edison, Incorporated, West Orange, N. J., a corporation of New Jersey Application August 8, 1947, Serial No. 767,482

1 6 Claims.

This invention relates to structural improvements in temperature-responsive resistor bulbs.

The invention is especially concerned with an improved terminal arrangement for connecting lead-out wires to the resistance element of such a bulb.

Objects of the invention are to provide an improved electrical terminal connectionv which is adapted for easy installation in resistor bulbs having very small size, which is easy to assemble and is cheap and rugged in construction, and which is adapted to permit heavy tugging on the lead-out wires while providing complete strain relief on the electrical resistance element.

The invention is particularly meritorious in connection with resistor bulbs having a sensitive end adapted for direct contact with the object whose temperature is to be measured and is herein illustrated in connection with such type of bulb, but it will be understood that the invention is applicable to various types of resistor bulbs.

In the description of my invention reference is had to the accompanying drawings, oi' which:

Figure 1 is a view, showing the casing in secition, of a resistor bulb incorporating my inven Figure 2 is a view of an internal unit of the bulb, with additional parts shown in dash-dot lines, taken on the line 2 2 of Figure 1;

Figure 3 is a detailed cross sectional view taken on the line 3--3 of Figure 1; and

Figure 4 is a View of one of the connecting terminals.

.The resistor bulb illustrative of my invention and shown in the accompanying drawings, comprises a cylindrical core I made of a highly heatconductive metal such as silver. To one end of this core there is secured, by means of a stud II, a cylindrical insulating body I2 made of a heat-resistant material such as a suitable ceramic. This insulating body has a larger diameter than has the core and provides a shoulder at one end of the core. At the other end of the core the same has an integral peripheral flange I3 to provide it with a second shoulder. Between these shoulders there is wound on the core a coil I4 of a resistance wire having a high temperature coeiiicient oi' electrical resistance.

In resistorbulbs which are to have a sensitive contactend, a contact button I5 is preferably provided integrally with the core beyond the flange I3, and an enclosing tubular casing IB is secured to the sensitive end of the core as to the flange I3. The casing may have an internal peripheral recess I'I adapted to receive snugly the flange I3 and may be secured to the flange by turning over an edge I8 of the casing about the flange. Additionally, the casing may be Welded to the ange. Preferably, the insulating body I2 has only a slightly less diameter than has the flange I3, so that it will t closely the inside wall ofthe casing and hold positively the core IIJ and coil I4 in spaced relation thereto.

The insulating body I2 is provided with two diametrically-opposite grooves I9 which extend lengthwise of the body. These grooves have end portions I9a of increased depth which are joined by a transverse slot 20 in the outer end of the insulating body. Also the insulating body has one peripheral groove 2I. These grooves are adapted to receive two electrical connector terminals 22 of which one is shown in Figure 4. The terminals are preferably made of stainless steel so as to have high mechanical strength and low heat conductivity. the low heat conductivity being important so that the terminals will not conduct heat readily from the temperature-responsive coil and cause any substantial lag in the response of the resistor bulb. Each terminal is provided with a longitudinally-extending member 23 adapted to lie in one of the longitudinal grooves I3 and with one or more side arms 24, two being preferred as shown, which are adapted to lie i'n the peripheral groove 2|, the shape of the terminal being thus that of a cross. Each terminal is mounted by laying it in the peripheral grooves as abovementioned with the head of the cross at the coil I4. After being so mounted,` the side arms are bent downwardly to conform to the bottom of the peripheral groove and then the terminals are secured in place by Winding an insulating heatresistant thread 25 around the body in the peripheral groove, a suitable thread being one made of iiber glass. It is of course understood that the side arms of the two terminals are not long enough to touch one another but that they need extend only a short distance along the peripheral groove so as to anchor the terminals to the insulating body lengthwise of the latter to provide a positive strain relief for the electrical resistance element as will appear.

At the upper end of each terminal there is a bifurcated lug 26 initially bent outwardly as indicated in Figure 2. A `lead 2'I of the electrical resistance coil is bared. and coiled about this bifurcated lug as in the manner illustrated in Figure 1, after which the lug is pressed inwardly within the longitudinal groove I9 and the wire is soldered to the terminal." The lower end of each terminal ends short of.v the insulating body and has two side lugs 29 bent inwardly into the groove portions [9a. The ends of lead-out wires 30 areNeXtended into the groove portions 19a between the side lugs 29 after which the side lugs are clamped onto the leads and secured thereto as by soldering. In order to accommodate an insulation 30a on the lead-out wires there is provided a transverse groove in the outer end portion of the insulating body.

In the manufacture of resistor bulbs, it hasV long been a problem to nnd a satisfactory terminal connection for the temperature-variable resistance element, which is simple, easy to assemble, and rugged, and which enables readily the lead-out wires to be positively electrically connected to the resistor element in a manner which will provide ample strain relief for the resistor element in applications where the bulb is subjected to an extreme degree of vibration such as in aircraft applications and the like. This problem is evident by the many different terminal connections which have been heretofore proposed. Applicant has found that the present terminal connector is superior to these foregoing connectors in that it is generally simpler, easier to install and assemble and in that it enables a positive connection to be made between the leadout wires and the resistor element which will provide the necessary degree of ruggedness and strain relief for the leads of the resistor element.

The embodiment oi my invention herein shown i's intended to be illustrative and not necessarily limitative of my invention since the same is subject to changes and modications Without departur from the scope of my` invention, which I endeavor to express accordingl to the following claims.

I claim:

1. A resistor bulb comprising a metal core of thermally-conductive material, a resistance element mounted on said core and having an electrical resistance variable with temperature, a casing enclosing said core and resistance element, a solid insulating piece joined to the outer end of said core and fitting closely the interior wall of said casing to hold the core and casing in spaced relation, said insulating piece being grooved at opposite sides along the length thereof and being also grooved transversely thereof, terminals lying in said lengthwise grooves and having side arms engaging said transverse grooves to anchor the terminals to the insulating piece in directions lengthwise of the latter, the inner` ends of said terminals being connected to said resistance element, and means surrounding said insul-ating piece to hold said terminals in place..

2. A resistor bulb comprising a metal core of thermally-conductive material, a coil of resistance wire wound on said core and having an electrical resistance variable with temperature, a hollow cylindrical casing enclosing said core and coil, a solid cylindrical heat-resistant insulating body secured to the outer end of said core, said insulating body having diametrically-opposite grooves lengthwise thereof and having also a peripheral groove, two terminals lying in said lengthwise grooves and having transverse arms lying in said peripheral groove, said terminals having the ends thereof adapted for lead connections thereto and the inner ends of said terminals being connected to said coil, and heat-resistant insulating thread wound around said body Within said peripheral groove to hold said terminals in place.

3. An internal unit for a resistor bulb, comprising a metal core of thermally-conductive material having a peripheral flange at one end, a heat-resistant insulating body secured to the other ends of said core and having'substantially greater dimensions in cross section than has said core, said insulating body having grooves length- Wise thereof and' a transverse peripheral groove intersecting said lengthwise grooves, said lengthwise grooves having portions of increased depth at the outer end of said body, and terminals mounted in said lengthwise grooves, each of said terminals having a cross arm engaging said peripheral' groove and having inwardly-projecting lead-connecting lugs at their outer ends disposed in said groove portions of increased depth.

4. An internal unit for a resistor bulb, comprising a metal core of thermally-conductive. material, a heat-resistant insulating body secured to one end of said core: and having a substantially greater cross sectional area than has the latter, said insulating body having grooves therein along the length thereof and having a peripheral groove intersecting said lengthwise grooves, terminals in saidlengthwise grooves having side extensions engaging said peripheral groove, said terminals being adapted atl the ends for lead connections thereto, and heat-resistant insulating thread wound in said peripheral groove to hold said terminals in place` 5, In a resistor bulb having a tubular casing; an internal resistor unit` comprising a metal. core of thermally-conductive material having an integral peripheral flange at one end, a cylindrical insulating body of heat-resistant material joined to the other end of said core, a coil of temperature-responsive wire wound on said core in the space between said flange and said insulating body, said body having diametrically-opposite grooves therein throughout the length thereof and having a peripheral groove, terminals in saidr lengthwise grooves joined at the inner ends thereof to said coil, said terminals having side arms lying in said peripheral groove, and a thread of` insulating heat-resistant material Wound about said insulating body within said peripheral groove to hold said terminals in place.

6. The resistor bulb set forth in claim 5, wherein each of said terminals has two side arms giving the terminal the shape of a cross, both of said side arms lying within said peripheral groove and having an overall length less than half the circumferential length of the peripheral groove.

GUSTAVE D. CERF.

- REFERENCES CITED The following references are of record in the iile of this pat-ent:

UNITED STATES PATENTS Number Name Date 954,350 Siler Apr. 5, 1910 1,350,910 Abbott Aug. 24, 1920 1,997,198 Ogg Apr. 9, 1935 2,008,288 Malone July 16, 1935 2,363,075 Mattern Nov. 2l, 1944 2,476,099 Knudsen July l2, 1949 

